The cytokine interleukin-10 (IL-10) is a dimer that becomes biologically inactive upon disruption of the non-covalent interactions connecting its two monomer subunits. IL-10 was first identified as a product of the type 2 helper T cell and later shown to be produced by other cell types including B cells and macrophages. It also inhibits the synthesis of several cytokines produced from type 1 helper T cells, such as γ-interferon, IL-2, and tumor necrosis factor-α (TNF-α). The ability of IL-10 to inhibit cell-mediated immune response modulators and suppress antigen-presenting cell-dependent T cell responses demonstrates IL-10 has immunosuppressive properties. This cytokine also inhibits monocyte/macrophage production of other cytokines such as IL-1, IL-6, IL-8, granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), and TNF-α. As a result of its pleiotropic activity, IL-10 is under investigation for numerous clinical applications, such as for treating inflammatory conditions, bacterial sepsis, enterotoxin-induced lethal shock, and autoimmune diseases, e.g., rheumatoid arthritis, allograft rejection and diabetes.
Cancers and tumors can be controlled or eradicated by the immune system. The immune system includes several types of lymphoid and myeloid cells, e.g., monocytes, macrophages, dendritic cells (DCs), eosinophils, T cells, B cells, and neutrophils. These lymphoid and myeloid cells produce secreted signaling proteins known as cytokines. The cytokines include, e.g., interleukin-10 (IL-10), interferon-gamma (IFNγ), IL-12, and IL-23. Immune response includes inflammation, i.e., the accumulation of immune cells systemically or in a particular location of the body. In response to an infective agent or foreign substance, immune cells secrete cytokines which, in turn, modulate immune cell proliferation, development, differentiation, or migration. Excessive immune response can produce pathological consequences, such as autoimmune disorders, whereas impaired immune response may result in cancer. Anti-tumor response by the immune system includes innate immunity, e.g., as mediated by macrophages, NK cells, and neutrophils, and adaptive immunity, e.g., as mediated by antigen presenting cells (APCs), T cells, and B cells (see, e.g., Abbas, et al. (eds.) (2000) Cellular and Molecular Immunology, W.B. Saunders Co., Philadelphia, Pa.; Oppenheim and Feldmann (eds.) (2001) Cytokine Reference, Academic Press, San Diego, Calif.; von Andrian and Mackay (2000) New Engl. J. Med. 343:1020-1034; Davidson and Diamond (2001) New Engl. J. Med. 345:340-350).
Methods of modulating immune response have been used in the treatment of cancers, e.g., melanoma. These methods include treatment either with cytokines such as IL-2, IL-10, IL-12, tumor necrosis factor-alpha (TNFalpha), IFNγ, granulocyte macrophage-colony stimulating factor (GM-CSF), and transforming growth factor (TGF), or with cytokine antagonists (e.g., antibodies). Interleukin-10 was first characterized as a cytokine synthesis inhibitory factor (CSIF; see, e.g., Fiorentino, et al (1989) J. Exp. Med. 170:2081-2095). IL-10 is a pleiotropic cytokine produced by T cells, B cells, monocytes, that can function as both an immunosuppressant and immunostimulant (see, e.g., Groux, et al. (1998) J. Immunol. 160:3188-3193; and Hagenbaugh, et al. (1997) J. Exp. Med. 185:2101-2110).
Animal models suggest that IL-10 can induce NK-cell activation and facilitate target-cell destruction in a dose-dependent manner (see, e.g., Zheng, et al. (1996) J. Exp. Med. 184:579-584; Kundu, et al. (1996) J. Natl. Cancer Inst. 88:536-541). Further studies indicate that the presence of IL-10 in the tumor microenvironment correlates with better patient survival (see, e.g., Lu, et al. (2004) J. Clin. Oncol. 22:4575-4583).
Because of its relatively short half life. IL-10 has been conjugated to various partners, including polyethylene glycol. Other cytokines have also been pegylated, generally via monopegylation, e.g., PEG molecules attached to a single residue on the cytokine protein. Unfortunately, monopegylation on one IL-10 subunit leads to a non-homogenous mix of dipegylated, monopegylated and nonpegylated IL-10 molecules due to subunit shuffling. Allowing a pegylation reaction to proceed to completion will also permit non-specific and multi-pegylated target proteins, thus reducing the bioactivity of these proteins. Thus a need exists to more efficiently produce correctly pegylated IL-10 with greater production yields. The present invention satisfies this need by providing methods of producing a mixture of mono- and di-pegylated IL-10.